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R1976
17-11-2009, 11:01 PM
Evening,

Could anyone recomend LP and HP switch settings for a 5 degree coldroom running on R404A. I have not yet used this gas, what pressures should I expect?

Also, if I have a second HP switch to control head pressure by bringing in a second condensor fan, how should I set this up ie. what pressure?

Any advice appreciated.

bill1983
17-11-2009, 11:12 PM
for lp settings, do you intend the unit to pump down when the coldroom is down to temperature, or are you using the lp switch to control the evaporating temperature?
for the hp what operating pressure was the system designed to run at? the condenser fan control should be designed to maintain that. does the fan cool he comp body or are you using a suction only cooled compressor.
your questions are not a straightforward as you think; give more information and we can help with better answers.

R1976
17-11-2009, 11:36 PM
Hi bill,

LP is for safety, compressor will shut down on temp by elliwell controller.

We have off cycle defrost, was planning to leave it default at 30 mins every 6 hours.

Hermetic Scroll compressor installed.

where do I find out design pressure?

Regards

FEISTY
18-11-2009, 04:14 AM
Design pressure information is usually on the condenser baseplate tag. Also make sure you don't have a headmaster control in place designed for head press use in outdoor situations. I have come across several " relocated units " that have controls that fight each other.

R1976
18-11-2009, 06:14 PM
Hi,

We don't have any other HP control. How do I set up the HP control switch? as we are in winter, should I set it just above the current condensing pressure and then in the summer it will come in on a high ambient?

What do you think should be the LP setting or should I run it constantly and see what pressure the evap ices up at and use this as a safety?

Regards

R1976
18-11-2009, 11:13 PM
Something I forgot to mention.

I have 40 metre pipe run, does this make a difference and is there anything I should do.

R1976
23-11-2009, 08:10 PM
Okay, systems now up and running.

I was wrong, we did use LP switch as a pump down to control the system but it was powered from the elliwell controller.

I set LP at 35psi, running pressure was 50psi, what does anyone think of that?

I am controlling head pressure at 230 - 250 psi.

Measured 60 psi at evaporater suction point and 6 degrees on suction pipe near compressor, suction superheat 26 degrees.

Coldroom comes down its 2 degree diff to 5 degree setting very quickly, about 10 mins. Then it takes about 10 mins for room to rise 2 degrees so compressor is on 10 mins then off 10 mins. Does this seem a bit much and is it a problem for the scroll compressor?

Would appreciate any advice from you seasoned coldroom engineers!

cadwaladr
23-11-2009, 08:30 PM
Okay, systems now up and running.

I was wrong, we did use LP switch as a pump down to control the system but it was powered from the elliwell controller.

I set LP at 35psi, running pressure was 50psi, what does anyone think of that?

I am controlling head pressure at 230 - 250 psi.

Measured 60 psi at evaporater suction point and 6 degrees on suction pipe near compressor, suction superheat 26 degrees.

Coldroom comes down its 2 degree diff to 5 degree setting very quickly, about 10 mins. Then it takes about 10 mins for room to rise 2 degrees so compressor is on 10 mins then off 10 mins. Does this seem a bit much and is it a problem for the scroll compressor?

Would appreciate any advice from you seasoned coldroom engineers!is there product in the room have you got curtains fitted,what product is it,how many times do personell enter,what temperature surrounds the outside of cold room,i would go for 3 diff until it settles down.

monkey spanners
23-11-2009, 10:08 PM
With your LP setting is 35psi the cut in or cut out pressure?

I'd set the cut in below the normal running pressure by 5 or 10psi to be sure it cuts back in, and the differential to between 20 and 30psi to stop it cycling too quickly. (some scrolls won't pump too low)

If its not a refrigerant i'm used to what i do is convert from one i am more familiar with, so if you are used to R22 write down the pressures you'd expect, convert these to temperatures with a slide rule or the markings on your gauges, then convert back from temperature to, in this case R404A.

You will probably be able to set the eliwell controller to delay switching for a few minute in one of the parameters if you are worried about the compressor cycling too frequently.

I think the copeland ones are allowed ten starts an hour for the smaller ones and six starts an hour for the bigger ones 7.5HP+

R1976
23-11-2009, 11:14 PM
Thanks Guys,

There is currently no product and the surrounding temp was 15 degrees. No one enters the coldroom as yet.

The coldroom is not your conventional type and was constructed by the builders. Its wall are standard plasterboard with 50mm thick coldroom foam panels, the roof is 10mm thick plastic with loft insulation packed above and the doors are standard wooden doors.

LP cuts out at 35psi with 10psi diff and compressor comes back on when liquid solenoid is energised.

I have set the compressor start delay to 3 mins.

old gas bottle
23-11-2009, 11:19 PM
depending on the product,set the diff to 3 deg,fine on most applications,helps with the defrost asswell, will cut the short cycling down,if the probes on the return air should still give good stable box temp.;) HP needs to be set quite high ,say 300psi unless there,s a CPR fitted as the start load will trip it in high ambient situations, LP set it with your gauges,the best and only sure way..:)

R1976
25-11-2009, 12:01 AM
Cheers all,

Old gas bottle, what do you mean by setting LP with gauges. The elliwell controller drops the feed to the liquid solenoid when the room is down to temp and this causes pump down?

Am I right to set it slightly lower than the running pressure, ie. 10-15 psi lower with 10 psi diff?

old gas bottle
25-11-2009, 08:48 AM
the diffs to tight it will short cycle,most engineers will tell you to stop the compressor just above "0"psi,that way it gives protection against pulling in air or moisure if a system fault occurs,the LP needs to trigger in again at about 30 psi,so fit you gauges and watch the operation by opening and shuting the reciever,i allways start at 20 psi and 20 diff but inevitbliy have to tweak the pressure setting up a bit [not the diff.] not every ones way but serves me well.;)

lice to chill
25-11-2009, 04:03 PM
i agree stop the compressor in positive pressure try setting the lp cut in first maybe at 2or5 degrees c[600 kpag /87 psig.may help your ice problems.

Rotax100uk
25-11-2009, 10:32 PM
i would set your
LP CUT OUT = 0psi
LP CUT IN = 20psi
HP CUT OUT = 350psi

thats only my opinion, others may vary tho, hope this helps

R1976
27-11-2009, 12:11 AM
Thanks for your replies.

Why do you set the LP cut out near 0 psi?

Wouldn't it be better to set it higher, at say 30 psi, then the compressor would not struggle to pump each time the coldroom gets down to temperature.

Can anyone explain?